Method and systems for a multi-fuel engine

Abstract

Various methods and systems are provided for a multi-fuel capable engine. In one example, a system comprises an engine having at least one cylinder controlled via an intake valve, a first fuel system to deliver liquid fuel and a second fuel system to deliver gaseous fuel to the at least one cylinder, a variable valve timing actuation system to adjust one or more of an opening or a closing timing of the intake valve, and a controller. The controller is configured to, during a liquid fuel only mode, adjust the variable valve timing actuation system to close the intake valve at a first timing based at least on engine load, and during a multi-fuel mode, adjust the variable valve timing actuation system to close the intake valve at a second timing.

The invention claimed is: 
     
       1. A system, comprising:
 an engine having at least one cylinder controlled via an intake valve; 
 a first fuel system to deliver liquid fuel to the at least one cylinder; 
 a second fuel system to deliver gaseous fuel to the at least one cylinder; 
 a variable valve timing actuation system to adjust at least one of an opening or a closing timing of the intake valve; and 
 a controller configured to:
 during a liquid fuel only mode where only liquid fuel is delivered to the at least one cylinder, adjust the variable valve timing actuation system to close the intake valve at a first timing based at least on engine load; and 
 during a multi-fuel mode where both liquid fuel and gaseous fuel are delivered to the at least one cylinder, adjust the variable valve timing actuation system to close the intake valve at a second timing, different than the first timing. 
 
 
     
     
       2. The system of  claim 1 , wherein the controller stores instructions in memory executable to:
 during the liquid fuel only mode and at a first engine speed and engine load point, adjust the variable valve timing actuation system to close the intake valve at the first timing, and 
 during the multi-fuel mode and at the first engine speed and engine load point, adjust the variable valve timing actuation system to close the intake valve at the second timing, and the second timing is earlier than the first timing. 
 
     
     
       3. The system of  claim 1 , wherein the controller stores instructions in memory executable to adjust the variable valve timing actuation system to close the intake valve at the first timing based at least on engine load and further based on one or more of peak cylinder pressure, ambient pressure, ambient temperature, exhaust gas temperature, or intake oxygen concentration. 
     
     
       4. The system of  claim 1 , wherein the controller stores instructions in memory executable to, during the liquid fuel only mode, close the intake valve earlier at higher engine loads and later at lower engine loads. 
     
     
       5. The system of  claim 1 , wherein the controller stores instructions in memory executable to, only at engine loads above a threshold load, adjust the variable valve timing actuation system to close the intake valve at the second timing that is earlier than the first timing. 
     
     
       6. The system of  claim 1 , wherein the second fuel system comprises at least one gas admission valve to control delivery of the gaseous fuel to the at least one cylinder, and where the at least one gas admission valve has a linear delivery operating region and a non-linear delivery operating region. 
     
     
       7. The system of  claim 6 , wherein the controller is further configured to, when operating in the multi-fuel mode, operate the at least one gas admission valve in the non-linear delivery operating region when engine output is less than a threshold output. 
     
     
       8. The system of  claim 6 , wherein the controller is further configured to:
 when operating in the multi-fuel mode with the at least one gas admission valve in the linear delivery operating region, determine an open duration for the at least one gas admission valve according to a gas mass equation in order to supply a designated amount of gaseous fuel to the at least one cylinder; and 
 when operating in the multi-fuel mode with the at least one gas admission valve in the non-linear delivery operating region, determine an open duration for the at least one gas admission valve according to a three-dimensional table in order to supply a designated amount of gaseous fuel to the at least one cylinder, the three-dimensional table specifying the open duration for the designated amount of gaseous fuel as a function of gaseous fuel density and a pressure ratio across the at least one gas admission valve. 
 
     
     
       9. The system of  claim 6 , wherein the controller is further configured to:
 when operating in the multi-fuel mode with the at least one gas admission valve in the linear delivery operating region, determine an open duration for the at least one gas admission valve according to a gas mass equation including a constant gas flow coefficient in order to supply a designated amount of gaseous fuel to the at least one cylinder; and 
 when operating in the multi-fuel mode with the at least one gas admission valve in the non-linear delivery operating region, determine an open duration for the at least one gas admission valve according to an adjusted gas mass equation including a variable gas flow coefficient in order to supply a designated amount of gaseous fuel to the at least one cylinder. 
 
     
     
       10. The system of  claim 6 , wherein the at least one cylinder is one of a plurality of cylinders, each cylinder supplied with gaseous fuel via a respective gas admission valve of a plurality of gas admission valves, and wherein the controller is further configured to, when operating in the multi-fuel mode and when engine output is less than a threshold output, provide gaseous and liquid fuel to only a subset of the plurality of cylinders to maintain each active gas admission valve in the linear delivery operating region. 
     
     
       11. A system, comprising:
 an engine having at least one cylinder controlled via an intake valve; 
 a first fuel system to deliver liquid fuel to the at least one cylinder; 
 a second fuel system to deliver gaseous fuel to the at least one cylinder; 
 a variable valve timing actuation system to adjust an opening and/or closing timing of the intake valve; and 
 a controller configured to:
 responsive to a ratio of gaseous fuel to liquid fuel reaching a first threshold ratio, adjust the variable valve timing actuation system to close the intake valve at a first timing prior to a piston of the at least one cylinder reaching a bottom dead center (BDC) position at an end of an intake stroke, further adjust the variable valve timing actuation system based on engine load; 
 responsive to the ratio dropping below the first threshold ratio but still above a second threshold ratio, adjust the variable valve timing actuation system to close the intake valve at a second timing, later than the first timing; and 
 responsive to the ratio reaching the second threshold ratio, adjust the variable valve timing actuation system to close the intake valve at a third timing, earlier than the second timing and later than the first timing. 
 
 
     
     
       12. The system of  claim 11 , wherein the second threshold ratio is zero gaseous fuel, and wherein the controller is configured to adjust the ratio to reach the second threshold ratio responsive to engine load exceeding a load threshold. 
     
     
       13. The system of  claim 11 , wherein the second timing is at BDC, wherein the first threshold ratio is a maximum substitution ratio with standard valve timing control, and wherein responsive to adjusting the variable valve timing actuation system to close the intake valve at the first timing, the controller is configured to increase the ratio above the maximum substitution ratio. 
     
     
       14. The system of  claim 11 , wherein the controller is configured to adjust the ratio to be below the first threshold ratio and above the second threshold ratio responsive to an indication of auto-ignition in the at least one cylinder. 
     
     
       15. The system of  claim 11 , wherein the controller is configured to adjust the ratio to be below the first threshold ratio and above the second threshold ratio responsive to intake manifold temperature exceeding a threshold temperature. 
     
     
       16. A method comprising:
 with a controller, during a liquid fuel only mode where only liquid fuel is delivered to at least one cylinder of an engine, the at least one cylinder controlled via an intake valve, adjusting a variable valve timing actuation system to close the intake valve at a first timing based at least on engine load, the engine having a first fuel system to deliver liquid fuel to the at least one cylinder, a second fuel system to deliver gaseous fuel to the at least one cylinder, and the variable valve timing actuation system that is configured to adjust at least one of an opening or a closing timing of the intake valve; and 
 with the controller, during a multi-fuel mode where both liquid fuel and gaseous fuel are delivered to the at least one cylinder, adjusting the variable valve timing actuation system to close the intake valve at a second timing, different than the first timing. 
 
     
     
       17. The method of  claim 16 , wherein adjusting the variable valve timing actuation system to close the intake valve at the first timing based at least on engine load comprises adjusting the variable valve timing actuation system to close the intake valve at the first timing during a first engine speed and engine load point, and wherein adjusting the variable valve timing actuation system to close the intake valve at the first timing comprises adjusting the variable valve timing actuation system to close the intake valve at the second timing at the first engine speed and engine load point, and the second timing is earlier than the first timing. 
     
     
       18. The method of  claim 16 , wherein adjusting the variable valve timing actuation system to close the intake valve at the first timing based at least on engine load comprises adjusting the variable valve timing actuation system to close the intake valve at the first timing based on engine load and further based on one or more of peak cylinder pressure, ambient pressure, ambient temperature, exhaust gas temperature, or intake oxygen concentration. 
     
     
       19. The method of  claim 16 , wherein the second timing is earlier than the first timing only at engine loads above a threshold load. 
     
     
       20. The method of  claim 16 , wherein the second fuel system comprises at least one gas admission valve to control delivery of the gaseous fuel to the at least one cylinder, and where the at least one gas admission valve has a linear delivery operating region and a non-linear delivery operating region, and the method further comprises, with the controller and when operating in the multi-fuel mode, operating the at least one gas admission valve in the non-linear delivery operating region when engine output is less than a threshold output.